Lens system, imaging device, and imaging system

A lens system for forming an image of light incident from an object side on an imaging element arranged on an image surface side, the lens system comprising:

• a plurality of lens elements including free-curved surface lenses;
• and a diaphragm arranged between the plurality of lens elements, wherein the plurality of lens elements form a front group arranged on the object side of the diaphragm, and a rear group arranged on the image surface side of the diaphragm, wherein a first lens element has an aspherical surface that is rotationally symmetrical, the first lens element being closest to the object side in the plurality of lens elements, wherein the free-curved surface lenses each has a free-curved surface that is asymmetrical with respect to a first direction and a second direction, and are arranged in the front group and the rear group respectively, the first and second directions crossing with each other, wherein a free-curved surface lens satisfying following conditional expression (i) is arranged on the rear group in the plurality of lens elements,
• D×(SV−SH)/IH>0.08 (1)
• where, IH:
• a height at which a ray with an angle of view of 300 forms an image on the image surface, in the first direction;
• SH:
• a sag amount at the height IH of the free-curved surface, in the first direction;
• SV:
• a sag amount at the height IH of the free-curved surface, in the second direction;
• and D:
• “1” in a case where the free-curved surface is on the object side of the free-curved surface lens, or “−1” in a case where the free-curved surface is on the image surface side of the free-curved surface lens.